Helper T cell (hereinafter to be referred to as “Th cell”) playing a central role in acquired immunity has been classified into Th1 cell involved in cellular immunity and Th2 cell involved in humoral immunity based on the difference in the cytokines they produce and the like.
In recent years, however, as a new Th cell subset different from Th1 cell and Th2 cell, Th17 cell has been identified as a Th cell that specifically produces IL-17 (non-patent document 1). The Th17 cell has been found to be involved in autoimmune diseases over a wide range such as multiple sclerosis, psoriasis, rheumatism, inflammatory bowel disease and allergic diseases such as contact hypersensitivity, atopic dermatitis and the like and, for example, in multiple sclerosis, it has been found using an animal model that Th17 cell is a stronger pathogenic cell than Th1 cell conventionally considered to be important (non-patent document 1, non-patent document 2, non-patent document 3, non-patent document 4).
Thus, while Th17 cell is drawing attention as a new target of autoimmune diseases, allergic diseases and the like, a drug that acts Th17 cell-selectively has not been developed yet.
For example, attempts have been made to treat autoimmune diseases by non-specifically suppressing lymphocyte infiltration into the lesion by using FTY-720 (fingolimod) and the like. However, discontinuation of medication has been reported to cause immediate aggravation of symptoms (non-patent document 5), and problems still remain.
Different from this approach, a efficacy of therapy has been reported in various autoimmune disease models, which is afforded by eliminating both Th17 cell and Th1 cell from the body by using an antibody having an ADCC activity (anti-lymphotoxin α antibody) (patent document 1). However, since both Th1 cell and Th17 cell are also involved in the biological defense (non-patent document 2, non-patent document 3), non-specific action (FTY-720) or inhibition of functions of both Th1 cell and Th17 cell could excessively decrease the biological defense function. Therefore, a pharmaceutical product that specifically acts on Th17 cell that shows a strong action as a pathogenic cell of autoimmune diseases has been desired.
To develop such a pharmaceutical product, for example, a molecule specifically expressed in Th17 cell may be used as a target. As a molecule specifically expressed in Th17 cell, RORγt which is a nuclear receptor, and the like have been identified (non-patent document 6), but Th17 cell-specific cell surface molecule has not been found (non-patent document 7).
Embigin is known as a single membrane-spanning protein that forms a family with CD147 (Basigin) and neuroplastin.
Embigin has been reported to be expressed in embryonic carcinoma cells (non-patent document 8), mouse fetal stage (early endoderm) (non-patent document 9), rat prostate, mammary gland, heart, liver, lung, brain (non-patent document 10), rat muscle (non-patent document 11), mouse hematopoietic cell (non-patent document 12). In addition, Embigin has been reported to show increased expression in rat hepatic fibrosis model (patent document 2).
Moreover, Embigin has been reported to be one of several thousand genes that vary on stimulation of CDC cell with anti-CD3 antibody/anti-CD28 antibody (patent document 3). However, this report is based on the comparison of a cell induced to differentiate into Th1 cell or Th2 cell and Th0 cell, and provides no description as to how Embigin varied in what cell, and completely no description as to Th17 cell.